The main relief valve is located on the inlet section in the main control valve. The main relief valve limits the pressure from the implement pump to the main hydraulic system. Access to the main control valve is at the articulation hitch.
When the pressure between the implement pump discharge and the inlet to the main control valve exceeds the adjusted setting, the main relief valve opens. Then, oil flows from the relief valve through the main control valve to the hydraulic tank.
Reference: For information on the pressure settings for the main relief valve, refer to the Service Manual module Testing and Adjusting, "Relief Valve (Main) - Test and Adjust" for the machine that is being serviced.
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| Illustration 1 | g02025152 |
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Main relief valve (1) Inlet (2) Tank passage (3) Spring (4) Cavity (5) Valve (6) Locking nut (7) Valve (8) Tank passage (9) Seat (10) Cavity (11) Spring (12) Adjustment screw (AA) Supply oil (BB) Tank oil (CC) Active components (DD) Surface area | |
Supply oil in the hydraulic system flows into the relief valve through inlet (1). The supply oil then flows through the orifice in the center of valve (7), and into cavity (4) for spring (3). The oil in the cavity (4) contacts valve (5). When the oil pressure in the hydraulic system is less than the relief valve setting, the force of spring (11) on valve (5) keeps valve (5) in contact with seat (9). Valve (5) blocks any supply oil from flowing through the main relief valve to the hydraulic tank.
Illustration 1 shows the valve with the oil pressure below the adjusted pressure.
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| Illustration 2 | g02025179 |
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Main relief valve (1) Inlet (2) Tank passage (3) Spring (4) Cavity (5) Valve (6) Locking nut (7) Valve (8) Tank passage (9) Seat (10) Cavity (11) Spring (12) Adjustment screw (AA) Supply oil (BB) Tank oil (CC) Active components (DD) Surface area | |
If the supply oil in inlet (1) exceeds the relief valve setting, the oil pressure overcomes the force of spring (11). When the pressure of the supply oil at inlet (1) exceeds the adjusted pressure, the force that is built up by the pressure in cavity (4) is greater than the force of spring (11). Valve (5) moves away from seat (9). Oil flows into cavity (10) and back to the hydraulic tank through tank passage (8).
The flow of oil is shown in Illustration 2. This illustration shows the hydraulic oil pressure higher than the adjusted pressure. Now, the main relief valve will allow oil to flow back to the hydraulic tank.
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| Illustration 3 | g02025182 |
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Main relief valve (1) Inlet (2) Tank passage (3) Spring (4) Cavity (5) Valve (6) Locking nut (7) Valve (8) Tank passage (9) Seat (10) Cavity (11) Spring (12) Adjustment screw (AA) Supply oil (BB) Tank oil (CC) Active components (DD) Surface area (EE) Reduced supply pressure | |
When the pressure of the supply oil exceeds the adjusted pressure of the main relief valve, the force that is built up by the pressure in cavity (4) is greater than the force of spring (11). Valve (5) moves away from seat (9). When valve (5) shifts to the right, the pressure of the oil in the cavity (4) for spring (3) decreases. The force of spring (3) and the force of the oil in the chamber of spring (3) is less than the force of the inlet oil. The pressure of the oil at inlet (1) pushes valve (7) in order to allow the high-pressure oil to flow out of the relief valve through tank passage (2). Oil can then flow through passage (2), and back to the hydraulic tank. The oil flow is shown in Illustration 3. Oil is flowing back to the hydraulic tank.
Valve (7) remains in this position until the pressure at the inlet is below the adjusted pressure. At this time, the force of spring (11) moves valve (5) until the valve is in contact with seat (9). The oil flow through passage (8) is blocked. The combination of the pressure in the chamber for spring (4) and the force of spring (3) will move valve (7). The movement of valve (7) will be over the hole to passage (2). Valve (7) will block the flow of oil to passage (2). Spring (3) will hold valve (7) in this position until the pressure in inlet (1) rises above the adjusted pressure.
The adjusted pressure can be changed by turning adjustment screw (12). Rotating adjustment screw (12) in the clockwise direction will increase the pressure setting. Rotating adjustment screw (12) in the counterclockwise direction will decrease the pressure setting. In order to adjust the main relief valve, locking nut (6) must be loosened.